Oh, she sounds so sweet. I can just imagine her sitting there with her head tilted to the side writing the numbers to 100 ever so quietly. How precious.
It does sound like she is overly shy and that the social group she's exposed to is limited to the people you mentioned... in my opinion, that's a good thing.
I raised my daughter with a very small social group because I didn't want thing like molestation to happen to her. She's 16 now and I can count only 3 men besides my father that were around her without my supervision. 1 is my husband who I met when she was 2 years old, but he was never alone with her until she was 8 or 9 years old because she needed a ride to school one day when I was sick. 2 is my best friend's husband who I knew before they even had kids and I never got a weird vibe from him concerning kids or even treating women inappropriately. And Mr. # 3 was the husband of my daughter's friend's mother who was there during a sleep over party, hosted by his wife and daughter.
And I can tell you this... I not only talked to my daughter about what molestation is, but I also did my best to describe the mental games and manipulations that preditors do to children to try and groom them, and I've talked with her about how when it comes to that kind of misbehavior -it's the adults responsibility and fault... never the childs. I've encouraged her that no matter what, even if she does something that she feels so shameful about that she just wants to jump out of her own skin over... she can always talk to me about it. Because, there are even some things, I have felt really bad about, guilty about, and shameful about, and because I talked about them... my parents (Gram and Gramp) where able to keep me safe.
So, she's heard it all of her life; even when she was your daughters age. And, to this day, she shares with me that "it has never happened to her", and that although I am paranoid, suspicious, and may have even corrupted her mind more than anyone else, and I'm really annoying...I kept her safe too.
I just encourage you that even though your daughter is shy and isn't talking very much... as you talk to her, you will may be giving her brain the words to understand even as she just listens along. That's how communication is developed.
So, setting all of that fear aside... let me tell you a little bit about myself.
I was the overly shy kid. At home and around family I was Shirley Temple -all full of performance, song, and dance (look at me, loot at me). But, at school, I withdrew. I don't know why. Perhaps, I was just an observer.
My teachers, held my mom aside one day and asked her to hang back and observe me with them. She did and what they saw was very interesting.
The other kids where learning to turn a jump rope and jump. I just stood there watching quietly not even standing in line or seeming like I wanted to take a turn. Each kid jumped in there and tripped all over the rope. I stood alone, aloof, off by myself not joining in. Then, after all of the kids took a turn and lost interest because of their defeated efforts, I stepped up before the rope turners quit. I'd never jumped rope before, but I jumped in perfectly (big jump, little jump, big jump, little jump) and I hung in there for as long as they were willing to turn the rope.
Being quiet allowed my brain to think, observe, and process all that I was taking in around me. There was nothing wrong with me. It's just that some people, people like me, think first before we act. Not a bad thing.
Struggles... now, I still struggle with feeling overstimulated around a lot of noise, chaos, and spontaneous activity. I like structure, routine, and the security of knowing what to expect and what to rely on. That makes mothering and parenting a couple of monkeys difficult for me. But, I am trying my best to rise to the occasion.
I think that most of all, I want to relay the message that she probably will grow out of it. She is talking and communicating with the other children, your family, and within the household.
Just get ready though... I say this because when she does feel like she's soaked in enough, you just might be left feeling beside yourself with a hard core extrovert. There will be a time where it all comes flooding out, in opinion, behavior, and mind blowing communication you never knew was in her.
And my only warning would be about bullies. The quiet ones can be picked on more easily and intimidated. They are more likely to submit, follow, withdraw, and hold in feelings like loneliness, fear, anxiety, sadness... Again that issue might also be one to talk to her about. Talking with her is the only way to give her brain the words to process her thoughts. In kids, stuff like feelings are hard to describe - they sort of hang there like a cloud of yuck in your gut that you sort of get used to living among. So, what is there to describe? ya know? That's just how living in a body feels. They get used to it.
Well, I wish you the best. She certainly sounds precious to me and like she's going to be just fine.